A pressure sensor device is typically mounted on a block, such as an automobile transmission oil-filled block, a hydraulic actuator block, or the like to measure pressure, and typically uses a semiconductor pressure sensor chip, applying a piezo-resistance effect as a sensor element. Such a semiconductor pressure sensor has an arrangement in which a plurality of semiconductor strain gauges are connected in a bridge circuit on a diaphragm made of a material, such as single crystal silicon, that exhibits a piezo-resistance effect. Deforming the diaphragm, due to a change in pressure, causes the gauge resistance of the semiconductor strain gauges to change in accordance with the amount of deformation. The amount of change is output from the bridge circuit as a voltage signal.
FIGS. 26-29 illustrate some known pressure sensor devices. The pressure sensor device shown in FIG. 26 is provided with a joint 1 having a threaded section, a flange member 3 for screwing the joint 1 into a section on which the device is installed, a pressure sensor 2 that outputs a voltage signal corresponding to the amount of change in the pressure as explained above, a circuit board 4 having mounted thereon a circuit chip for processing the output signal from the pressure sensor 2, wire bonding 5 connecting the pressure sensor 2 and the circuit board 4 together, and terminals 6 and 7 for outputting the signal from the circuit board 4 to the outside. The terminal 6 and a terminal stand 8, which supports the terminal 7, are secured to the flange member 3 by a joining member 11. Moreover, a gasket 9 and an O-ring 10 are assembled onto the joining member 11. See for example FIG. 1 of Japanese Patent Application Laid-open No. 2002-168718.
The pressure sensor device shown in FIG. 27 is composed of a transducer 12, a hexagonal port 13, a cover 14, an annular sealing gasket 15, a periphery clip 16, a flexible circuit 17, and a base member 18 for outputting a signal to the outside. The transducer 12 is composed of a first conductive film that deforms upon being subjected to pressure, a second conductive film facing the first conductive film with a spacer therebetween, and a circuit for converting an electrostatic capacitance that changes through the deformation of the first conductive film into a voltage signal. See for example FIG. 1 of Japanese Patent Application Laid-open No. 2002-202215.
The pressure sensor device shown in FIG. 28 has an arrangement in which, in a sensor case 24 to which are secured connecting leads 19, 20, 21, and 22 that are insulated by hermetically sealing glass 23, a pressure sensor chip 25 is connected to the connecting leads 19, 20, 21, and 22, and the pressure sensor chip 25 is encapsulated in silicone oil by a metallic diaphragm 26. Moreover, the pressure sensor device is protected from above by a metallic hard cover 27. See for example FIGS. 8 and 10 of Japanese Patent Application Laid-open No. 2000-55762.
The pressure sensor device shown in FIG. 29 has an arrangement in which the pressure sensor device shown in FIG. 28 is housed in a metallic housing 28 using an O-ring 29, and a connector housing 33, having therein terminal boards 30, 31, and 32 that are electrically connected to the connecting leads 19, 20, 21, and 22, is crimped onto the metallic housing 28, with an O-ring 34 and a spacer ring 35 for securing thereto. The metallic housing 28 has a pressure receiving port 36, a threaded section 37, a fastening section 38, and a stepped portion 39. See for example FIGS. 8 and 10 of Japanese Patent Application Laid-open No. 2000-55762.
Moreover, it is known, in a semiconductor pressure sensor, to incorporate an amplifying circuit for an output signal from piezo-resistors. The amplifying circuit is formed from a combination of an operational amplifier and a resistance network comprising thin film resistors integrated on a semiconductor element having a diaphragm section on which the piezo-resistors are formed. In a sensor device using such a semiconductor pressure sensor, the semiconductor pressure sensor is housed in a sealed container. In the container, the space on a side faced by a surface of the semiconductor pressure sensor is kept at a constant pressure. Thus, an arrangement is provided such that the pressure applied to the back of the semiconductor pressure sensor is measured via a pressure introducing port in the container, with the pressure in the container being taken as a reference. See for example Japanese Patent Application Laid-open No. 1-150832.
In the pressure sensor devices shown in FIGS. 26 and 27, however, numerous parts raise the material and assembly costs. Moreover, in each of the devices, the signal transmission path is made up of numerous parts that require numerous connections therebetween. Specifically, in the device shown in FIG. 26, the signal transmission path includes the pressure sensor 2, the wire bonding 5, the circuit board 4, the circuit chip, the terminal 6, and the terminal 7. In the device shown in FIG. 27, the signal transmission path includes the transducer 12, the flexible circuit 17, the circuit chip, and the base member 18. This increases the failure probability, causing long-term reliability problems. Furthermore, in the device shown in FIG. 26, the direct joint of the joint 1 and the pressure sensor 2 can cause stress, such as when screwing the joint 1, and transmits to the pressure sensor 2. This lowers the accuracy and reliability of the measured signal.
Moreover, in the pressure sensor device shown in FIG. 28, the silicon oil can become polarized by the external noise applied to the terminals and the outside, which can causes electric charges to accumulate on the surface of the pressure sensor chip 25. This can vary the signal output from the pressure sensor chip 25 and lower the reliability of the measured signal. Moreover, an increase in an inner pressure due to expansion of the silicon oil under a high temperature environment and compression of the silicon oil when applying a high pressure produces repeated stresses in the metallic diaphragm 26. This fatigues the metallic diaphragm 26, which is becomes problematic with the long-term reliability. Moreover, in the pressure sensor device shown in FIG. 29, the large area of the section for receiving pressure results in a large applied load to the device. For supporting such a load, rigidity of the metallic housing 28 must be increased. This increases the cost and size of the device.
Moreover, in the pressure sensor device disclosed in Japanese Patent Application Laid-open No. 1-150832, the external signal terminals for outputting output signals to the outside are glass-sealed at the bottom of the container, and hence the container is assumed to made of metal. The metal container, however, has the disadvantage of being expensive. Furthermore, the external signal terminals and a pressure introducing port are provided on the same side. Therefore, when the pressure sensor device is used for measuring the pressure, while mounted on an oil-filled block, an actuator block or the like, the external signal terminals interrupt the pressure sensor device, making it difficult to mount the pressure sensor device. Therefore, the external signal terminals must be projected on the side opposite to the side on which the pressure introducing port is provided. However, as explained above, when the container is metallic, it is difficult to provide the external terminals on the opposite side of the pressure introducing port.
There still remains a need for a pressure sensor device that can be manufactured with a low cost, have a high long-term reliability, and with measured signals of high accuracy and reliability, and in particular with external terminals disposed on the opposite side of the pressure introducing port. The present invention addresses this need